This invention relates to an improved system and method for acoustically detecting gradually occurring cutting tool breaks without false alarming on cuts commonly encountered in machining operations.
A tool break sensing system for lathes and other machine tools, based upon recognition of characteristic acoustic signatures in preprocessed cutting noise vibration signals, has been developed and is disclosed in several commonly assigned copending applications. The usual tool break signature is a large, abrupt, increase or decrease in signal level. Then a new type of tool break signature began occurring and a feature was added, without changing the firmware significantly, to give an alarm whenever the mean signal falls below a lower limit and remains below for at least a minimum time period. This feature permitted detection of the new gradual-decrease tool break signatures, but also caused false alarms on all ends of cut and on some other metal-to-air transitions of the tool path. These false alarms can often be ignored by the machine tool control on the basis of information in the part program as to when such metal-to-air transitions will take place. However, there are cases where this cannot be done and the gradual-decrease tool break signature recognition logic must be disabled, thus causing missed tool breaks. These types of tool breaks, that produce major cutting condition changes occurring over a period of time, are expected to remain a problem of some significance.
The foregoing break detection logic is more fully described in application Ser. No. 685,005, now U.S. Pat. No. 4,642,617, filed Dec. 21, 1984, C. E. Thomas et al, "Acoustic Tool Break Detection System and Method". The technical paper "Automatic Tool Touch and Breakage Detection in Turning", S. R. Hayashi et al, Sensors '85, Nov. 5-7, 1985, Detroit, discloses the integrated touch and break detector.